1. Field of the Invention
The present invention relates to a low temperature polysilicon film. More particularly, the present invention relates to a method for controlling the nucleation position of the crystallization of the low temperature polysilicon film.
2. Description of the Related Art
In the development of the process of the thin film transistor (TFT) liquid crystal display (LCD), a technology of low temperature polysilicon TFT has become a trend in recent years. The technology of low temperature polysilicon TFT is a novel TFT technology compared with conventional amorphous silicon TFT. The electronic mobility of the novel TFT technology has been at least up to 200 cm2/V-sec, and therefore the size of the chip area is reduced and the aperture ratio is increased. Moreover, because of the enhancement of the electronic mobility of the novel TFT technology, a part of the driving circuit can be manufactured on the glass substrate along with the TFT manufacturing process. Thus the cost of the novel TFT technology is much lower than that of the conventional amorphous silicon TFT. In addition, because the LCD produced with the low temperature polysilicon TFT has a thinner thickness, a lighter weight and a higher resolution in comparison with the LCD produced with conventional amorphous silicon TFT, the novel technology is especially applicable for electronic products that are power saving, handy, and portable.
In the conventional manufacturing process of the low temperature polysilicon TFT, the manufacturing method of the low temperature polysilicon film includes the steps of forming an amorphous silicon layer on the substrate by a chemical vapor deposition (CVD) method and of directly proceeding with a laser crystallization process. However, the nucleation position of the crystallization process is not under control in the conventional laser crystallization process of transforming the amorphous polysilicon film to the polysilicon film. In addition, the grain sizes of the crystal are not uniform after the laser crystallization process, thus the number of grain interfaces in the channel of each TFT will be different, and if the number of grain interfaces in the channel is too large, the electric property and the stability of the TFT will be reduced.